I know someone who is making a lot of extra money outside the school teaching/etc.

Its my understanding that the most opportunities for private teaching, etc. is in Saudi Arabia. However, I just want to get others opinions. If one wants to make extra money doing whatever (private instruction, etc.) are all the major countries with teachers (SA, Bahrain, Oman, UAE, etc.) the same or is one of them the best?

Qatar and UAE are probably more lucrative, simply because there's more $$. However, be very aware it is illegal to take on private students WITHOUT your sponsor's permission - and most contracts specifically state you are not allowed to work for anyone else.

Do people do it? Sure. Is it likely you'd be caught? Probably not - but it only takes one disgruntled customer or colleague to dob you in and then you're out of luck.

I teach adults and they are forever asking me to teach their kids. I never do. But most work in KSA is teaching teenagers and the chances of them asking for extra lessons are non-existent. When most of them have to be paid to attend classes, they're not likely to spend that money on further education.

Every now and then I see an advert looking for a private teacher or an Indian offering any manner of lessons. I wouldn't bank on it being a regular source of income.

With regards to teaching private lessons to ME adult and Saudis in particular, it seems they have unrealistic expectations as to what they hope to achieve by taking private lessons. In my brief experience teaching one to one private lessons is that most are not very reliable and do not bother to show up or bother to call to cancel, or they come late...also they seem not to be keen with any structured lessons, perhaps it reminds them too much of their school days but rather prefer to practice their conversation informally. Sometimes I wonder, if they think they will learn English by just sitting in the same room as an English speaker without having to say a word They like the idea of learning, but are not so willing to put in the effort...at least this was my experience...you could spend lots of time preparing for a lesson and then they do not bother to show up...or you waste time waiting for them to show up... I gave it up and now just teach overtime at the university where I work. They often offer extra evening courses or external contracts at the university. At least that way you are more likely to get paid and do not have to bother with all the nonsense of negoiating fees and recruiting students. The university does all that. You just show up and teach them.
If you are gung-ho on private lessons...you most likely will end up negoiating a price on a case by case basis...but the cheaper you go the less reliable they may be...but if you charge higher fees, you better be doing a few back flips for them to warrent the high fees...